Various articles, including biomedical devices, are formed of organosilicon-containing materials. One class of organosilicon-containing materials useful for biomedical devices, such as soft contact lenses, is silicone-containing hydrogel materials. A hydrogel is a hydrated, crosslinked polymeric system that contains water in an equilibrium state. Hydrogel contact lenses offer relatively high oxygen permeability as well as desirable biocompatibility and comfort. The inclusion of a silicone-containing material in the hydrogel formulation generally provides higher oxygen permeability since silicone based materials have higher oxygen permeability than water.
Organosilicon-containing materials useful for biomedical devices, including contact lenses, are disclosed in the following U.S. Pat. No. 4,208,506 (Deichert et al.); U.S. Pat. No. 4,686,267 (Ellis et al.); U.S. Pat. No. 5,034,461 (Lai et al.); and U.S. Pat. No. 5,070,215 (Bambury et al.).
U.S. Pat. Nos. 5,358,995 and 5,387,632 describe hydrogels made from various combinations of silicone macromers, TRIS, n-vinyl pyrrolidone (NVP) and DMA. Replacing a substantial portion of the silicone macromer with TRIS reduced the modulus of the resulting hydrogels. Two publications from the same author, “The Role of Bulky Polysiloxanylalkyl Methacrylates in Polyurethane-Polysiloxane Hydrogels”, J. Appl. Poly. Sci., Vol. 60, 1193-1199 (1996), and “The Role of Bulky Polysiloxanylalkyl Methacrylates in Oxygen-Permeable Hydrogel Materials”, J. Appl. Poly. Sci., Vol. 56, 317-324 (1995) also describe experimental results indicating that the modulus of hydrogels made from reaction mixtures of silicone-macromers and hydrophilic monomers such as DMA decreases with added TRIS. The addition of methacryloxypropyltris(trimethylsiloxy)silane (TRIS) reduced the modulus of such hydrogels, but in many examples the modulus was still higher than may be desired.
U.S. Pat. No. 4,208,506 describes monomeric polyparaffinsiloxanes end-capped with activated unsaturated groups and polymers and copolymers thereof. The monomers of U.S. Pat. No. 4,208,506 are cross-linkers. We have discovered that mono ethylenically unsaturated polycarbosiloxane monomers are advantageous in device forming monomer mixes because in addition to reducing the crosslink density of the polymerized mixture the additional chain length of the alkyl portion of the monomer backbone reduces the modulus of the polymerized monomer mix.
There still remains a need in the art for silicone hydrogels which are soft enough to make soft contact lenses, which possess high oxygen permeability, suitable water content, and sufficient elasticity, and are comfortable to the contact lens wearer.